The long and extensive use of ammonium sulphate on a soil has a tendency to produce an acid condition, through the accumulation of sulphates which: are not largely taken up by plants. Ammonium sulphate, like sodium ni trate, should not be applied in autumn, as the ammonia is converted into nitrates and leached from the soil.
Chemical Processes for the Fixation of There are now several chemical processes for the fixation of atmospheric nitro gen, two of which are well known and were in use on a commercial scale before the out break of the present war, the others are more recent, and exact knowledge regarding them is rather difficult to obtain.
Calcium The fertilizers pro duced by the older processes are calcium cya namid and calcium nitrate. The former is sold in this country under the trade name °Cya namid?' One process for its production con sists in passing nitrogen into closed retorts con taining powdered calcium carbide heated to a high temperature; the product being calcium cyanamide and free carbon :— In preparing the calcium carbide for this process it must be ground out of contact with air. The nitrogen required for the process is obtained either by passing air over heated cop per, or by the fractional distillation of liquid air.
The fertilizer, as placed on the market, is a heavy black powder or granulated material with a somewhat disagreeable odor, the dark color being due to the carbon set' free in the process and which remains distributed in the cyanamid.
Cyanamid as manufactured in this country has about the following composition: According to this composition the material would contain 16 per cent of nitrogen. Lime in the form of carbonate and hydroxide would add something to its value, and the residue of calcium cyanamide, which upon decomposition becomes calcium hydroxide, is likewise bene ficial to the soil.
Calcium cyanamide must decompose in the soil before its nitrogen becomes available to plants. There are several steps in the decom position process by which the nitrogen finally emerges in the form of ammonia. The inter mediate products formed during decomposition will vary somewhat with the condition of the soil. When, for instance, a soil is saturated with water, or when it is acid some more or less injurious substances may be formed. For this reason "cyanamid" is not likely to be so satisfactory on soils of this nature as on better soils. To very sandy soils it is not well suited.
Under good conditions its fertilizing value is not greatly below that of sodium nitrate and is about equal to that of ammonium sulphate when not used in heavy applications.
It should be incorporated with the soil at least a week before planting,, as it may injure the young plants if decomposition has not pro ceeded far enough to remove its somewhat toxic properties. As it must undergo this de composition before its nitrogen becomes avail able to young plants, there is an added reason for this precaution. It does not give its best results as a top-dressing because it requires incorporation with the soil for its proper de composition.
Other Fixation Processes.— The first com mercial process for the fixation of nitrogen was the arc process. Its use, however, is .confined to Norway where 250,000 kilowatts of electricity are employed in its use. By this process nitro gen and oxygen are directly burned to nitric acid under the influence of the electric arc. The resulting product is nitric acid, which is neutralized with lime forming calcium nitrate, a fertilizer somewhat similar to nitrate of soda. Owing to the enormous electrical power required the operation is an expensive one unless the electricity can be cheaply developed, as when water power is abundantly available, which is the case in Norway. It does not seem likely that the process will be extensively adopted in this country.
There are several very promising processes that have been brought forward since the be ginning of the pretent war, but which on ac count of the great demand for explosive coin binations of nitrogen have not been applied to the production of fertilizers.
Organic Carriers of Nitrogen.— Organic nitrogenous fertilizers include cotton-seed meal (7 per cent nitrogen when free from hulls), linseed meal (5.5 per cent nitrogen), castor pomace (6 per cent nitrogen), and a number of refuse products from packing houses, consist ing of red-dried blood (13 per cent nitrogen), black-dried blood (6 to 12 per cent nitrogen), dried meal (13 per cent nitrogen), hoof-meal (12 per cent nitrogen), ground fish (8 per cent nitrogen), and tankage (concentrated 10 to 12 per cent, crushed, 4 to 9 per cent nitrogen), also leather-meal, and wool-and-hair waste, which last two on account of their physical condition are of little value.